Diffusion of Na atoms on a Cu(001) surface

We study the equilibrium properties and the diffusive motion of Na atoms adsorbed on a Cu(001) surface at finite coverages via a model Hamiltonian. Our model Hamiltonian starts with an adatom-substrate interaction potential based on the previous analysis of the zerocoverage He scattering data. The dipole-dipole interaction between the alkali adatoms at finite coverages is then included. We use Monte Carlo simulations to study the ordered structure of the system at low temperatures and molecular-dynamics simulations for evaluating the dynamical correlation functions relevant for both the tracer and collective diffusive constants.